The Raman engine computes NLI just for a subset of channels; this is an
important speed optimization because the computation is rather CPU
heavy. However, the code just left NaNs in place for NLI of those
channels which were not explicitly simulated.
This is wrong because these NaNs propagate all the way to the total
input/output powers per the whole spectrum, etc, leading to NaNs being
shown to the user.
This patch uses a very simple linear approximation just in order to
prevent these NaNs.
fixes#288
Both of these places referred to "eq. 123 from arXiv:1209.0394", the
only difference (apart from the source of the input parameters, beta2
and asymptotic_length) was calling the two branches "SCI" and "XCI" vs.
"SPM" and "XPM".
In this commit I've only moved the code to a single implementation. The
input data are still being read from the same parameters, of course.
Conceptually, this is just about propagating the input parameters (which
drive the simulation) into all RamanFiber instances. The network module
already contains similar functions, let's move it there.
